This invention relates to electronic circuits, and in particular to a type of circuit which allows switching of an output signal quickly upon the arrival of a particular input signal.
In the design of asynchronous circuitry, it is desirable to provide circuits which switch very quickly after arrival of a particular input signal, frequently referred to herein as the "critical" input signal. For example, the designer of a system will often be aware that a particular input signal typically arrives last among a group of input signals. It is therefore desirable to allow the system to react as quickly as possible to that last arriving critical signal so that the next operation to be performed can start as soon as possible.
One well known circuit which lacks this capability, but which is of similar form, is a carry chain circuit such as found in an adder. A carry chain circuit typically consists of an inverter coupled to receive an input carry bit together with suitable logic coupled to the inverter to receive the bits to be added. In a multiple bit adder many such circuits are serially connected to each other, enabling the carry bit to propagate from stage to stage. An example of this circuit is described by Neil H. E. Weste and Kamran Eshraghian in Principles of CMOS VLSI Design - - - A Systems Perspective, Addison-Wesley Publishing Co., Reading, Mass. (1988), pp. 311-314.